In most heat-production installations using a liquid fuel of the type referred to above, three essential parts can be defined: a ventilated storage tank with a filling port and level control, a pressure unit with all the automatic components, safety devices and filters and suction and delivery piping, usually not more than 15 mm in diameter as only the fuel used by the burner is delivered, soft copper piping being the most commonly used to avoid welds and sleeves and, finally, the associated burner.
A pressure relief valve is fitted alongside the burner, incorporating a pressure gauge to indicate the output pressure so that each burner manufacturer can adjust the value to provide the optimum pressure for each type of burner and so avoid damage to its components. On the other hand, suction problems with the pump incorporated into each burner are avoided.
If the burner includes return, this is delivered through the pipe between the pressure relief valve and the pressure unit: the relief valve limits excess pressure in the burner both while operating and while stopped.
The nozzle circuit, loop circuit and direct burner suction systems are familiar burner feed systems.
The nozzle circuit is considered to be the most effective of these, as it facilitates burner suction, removes air pockets, and suction pressure is minimal. On the other hand, it is very expensive to install.
Pressure in the loop circuit cannot be controlled and an electric pump is required, to operate non-stop. Pipe diameters are usually 42 mm. A return is required to the tank and it is not possible to eliminate air pockets. If pipes break, the fuel in the general tank may spill, with risk of fire or water contamination.